In recent years, the image collection apparatus for collecting and monitoring an image of an installation place which is picked up by the installed video camera or the like has been increasingly required according to the necessity. As a conventional prior art related to such an image collection apparatus, for example, Japanese Patent Application Laid-Open No. 10-240774 discloses a data collection method and monitoring apparatus. In this apparatus, images of an event are stored just before and after the time at which the event is generated. Thus, a lot of events can be stored even if the storage capacity is small. The conventional image collection apparatus will be explained below with reference to the this apparatus.
FIG. 28 is a block diagram showing the entire structure of the conventional image collection apparatus. A plurality of local devices 101, a plurality of center devices 102, and a data management device 103 are connected to each other through a network 105 and can mutually transmit and receive information. The local devices 101 are placed at places that are to be monitored. The center devices 102 are placed at a place where a supervisor (a person who is authorized to monitor) is present. A display device 106 is provided to each center device 102, which can display the image information or reproduce voice information for the supervisor. The local device 101 has a video camera, which acquires image information and voice information. The local device 101 stores the acquired information in a storage device 104. The data management device 103 intensively manages stream index information about the location of information (stream data) recorded in a media on the network 105, for example, the storage device 104. The center device 102 retrieves the stream data index information based on certain retrieval conditions, obtains the result of retrieval for the location of the stream data to know the location of the stream data satisfying the retrieval conditions and collects stream data satisfying the retrieval conditions from the media.
A data input unit 107 digitizes the acquired image information and voice information. The image information is coded into MJPEG (Motion Joint Photographic Coding Experts Group) or MPEG (Motion Picture Experts Group) and the voice information is coded into PCM (Pulse Code Modulation) and ADPCM (Adaptive Differential Pulse Code Modulation). An input data storage and read unit 108 stores the coded data as timely continuous stream data in the storage device 104. In addition, the input data storage and read unit 108 transmits the stored stream data through a communication unit 109 and the network 105 according to a request from the center device 102 through the network 105.
In this case, the input data storage and read unit 108 generates stream data index information causing the input image information and voice information to correspond to the generated event, and stores the stream data index information in the storage device 104 and transmits the same to the data management device 103. In the case in which desirable image information or the like is fetched as described above, the stream data index information stored in the data management device 103 is used.
The input data storage and read unit 10B stores, as event information, the stream data on the image information and the voice information for only a predetermined time before and after the generation of the event. For instance, FIG. 29 shows an example of the stream data index information. As shown in the column of recording time duration in the stream data index information D1, image of the event 300 seconds before the generation of the event and 300 seconds after the generation of the event is stored. The stream data index information D1 includes event ID, type of the event, information about coding, information about the input device and the local device which picked the image, and the like.
FIG. 30 is a diagram showing the recording state of an event image corresponding to the stream data retrieval information D1 in FIG. 29. Three local devices Loc03, Loc08 and Loc10 independently pick up images and record, as event images 111a to 111c, 300 seconds before and after the time at which an event is generated on the time base of each of all picked up images 112a to 112c. More specifically, the local devices Loc03 and Loc08 store the event images 111a and 111b at the same time for an event having an event ID of Ev003. For an event having an event ID of Ev006 generated later, the local device Loc10 stores the event image 111c. Thus, only images picked up before and after the time of the event generation are stored. Consequently, even if the storage device 104 has a limited storage capacity, a lot of information can be stored. An event here means an event occurring instantly and does not have a time width. The same definition holds in the following description.
However, the conventional image collection apparatus stores the image picked up for a predetermined time mainly including the time at which an event is generated. Thus, individual event images are stored independently of other event images. If a group of related events is to be retrieved, a lot of time is required for the retrieval operation. Even if it is considered that the retrieval operation does not require long time, it is difficult to grasp the relationship of the events in the group on a time basis. Thus, there is a disadvantage that it requires time and labor to carry out the monitoring or analysis.
These problems are explained in detail with respect to FIG. 31 and FIG. 32. FIG. 31 shows the relationship between an event image including a series of related event images and an event. In the whole image 112 in FIG. 31, five events of entry into and leaving from a room, that is events 121 to 125 (event ID: 1 to 5), are generated and event images 113 to 117 are recorded corresponding to the events 121 to 125. Accordingly, when events are retrieved with the type of the event as “entry”, for example, the event images 121, 122 and 124 can be fetched and referred.
Consider, as shown in FIG. 32, that the events 121 and 123 correspond to entry and leaving of the same employee (employee No. 122). In this case, it is impossible to refer to a macro event image 141 corresponding to a bigger event (which will be hereinafter referred to as macro event) which is an event having a time width the vicinity of a time including the time of the generation of the event 121 at which this employee enters the room to the vicinity of a time including the time of the generation of the event 122 at which this employee leaves the room. Similarly, consider that the events 122 and 125 correspond to entry and leaving of different employee (employee No. 155). In this case, it is impossible to refer to a macro event image 142 corresponding to a macro event having a time width from the vicinity of a time including the time of the generation of the event 122 at which this employee enters the room to the vicinity of a time including the time of the generation of the event 125 at which this employee leaves the room.